Two submersible data-loggers for phosphate and nitrate are available that allow high-frequency measurement of nutrient concentrations in watercourses.

The Cycle PO4 Phosphate Sensor (below left and centre) is a submersible, phosphate analyser with built-in data logger that provides unparalleled precision and accuracy. Ideal for unattended monitoring the Cycle PO4 includes keyed, pre-mixed on-board reagent cartridges and calibration standards that click into place. Each set of reagents is sufficient for just over 1000 measurements.
It uses the established ‘molybdenum blue’ method. A small volume of sample is filtered and drawn in by precision micro-pumps, reagents are injected and mixed – if there is phosphate in the sample a blue colour will develop. The higher the phosphate concentration the deeper the colour. The controller software is easy to use but the unit should be set up by an expert user. Ongoing maintenance can be done by anyone.

The SUNA V2 Submersible Ultra-Violet Nitrate Analyser (below right) is a submersible sensor for the measurement of nitrate concentrations in water. It has built-in data-logging and can be fitted with an automatic cleaning unit to enable long-term, unattended deployments. It can be easily interfaced to telemetry units to enable remote collection of data.

The SUNA V2 uses the chemical-free ultraviolet absorption principle to measure nitrate. It is available with 10cm and 5cm path-lengths and uses adaptive sampling techniques (adjusts the light source in response to turbidity) so that it can be used in more optically challenging environments.

The SUNA is best operated by someone with at least some previous experience with water quality sensors. Training and instruction and ongoing support is provided.